Choriogenin mRNA induction in male medaka, Oryzias latipes as a biomarker of endocrine disruption

Toxic effects of environmental concentration Bisphenol AF exposure on the survival, growth and reproduction of adult male Oryzias curvinotus

Bisphenol AF (BPAF) is a novel environmental endocrine disruptor, and is widely detected in the aquatic environment, which is a potential threat to the health of fish. In this study, male Oryzias curvinotus were exposed to environmental concentrations (0.93 and 9.33 μg/L) of BPAF for 21 days. The effects of BPAF on survival, growth, reproduction, liver and testis histology, and gene transcriptional profiles of O. curvinotus were investigated. The results showed that the survival rate of male O. curvinotus slight decrease with increasing BPAF concentration, and there was no significant effect on body length, body weight, and K-factor. BPAF (9.33 μg/L) caused significant changes in testicular structure and reduced spermatid count in O. curvinotus. Changes in transcript levels of some antioxidant-related genes in gills and liver following BPAF exposure, imply an effect of BPAF on the immune system. After BPAF exposure, chgs and vtgs were up-regulated, validating the estrogenic effect of BPAF. In the hypothalamic - pituitary - gonadal axis (HPG) results, erα, erγ and cyp19a1b were all up-regulated in the brain, and the 0.93 μg/L BPAF group was more up-regulated than the 9.33 μg/L BPAF group. In testis, BPAF significantly up-regulated the mRNA expression level of cyp17a1 and cyp11b, while significantly down-regulated mRNA expression level of cyp11a, and cyp19a1 was significantly down-regulated only in the 0.93 μg/L BPAF group. In conclusion, environmental levels of BPAF have adverse effects on the survival and reproduction of O. curvinotus, and the potential toxic effects of environmental levels of BPAF cannot be ignored.

A systematic review of the evaluation of endocrine-disrupting chemicals in the Japanese medaka (Oryzias latipes) fish

Japanese medaka (Oryzias latipes) is an acceptable small laboratory fish model for the evaluation and assessment of endocrine-disrupting chemicals (EDCs) found in the environment. In this research, we used this fish as a potential tool for the identification of EDCs that have a significant impact on human health. We conducted an electronic search in PubMed (http://www.ncbi.nlm.nih.gov/pubmed) and Google Scholar (https://scholar.google.com/) using the search terms, Japanese medaka, Oryzias latipes, and endocrine disruptions, and sorted 205 articles consisting of 128 chemicals that showed potential effects on estrogen-androgen-thyroid-steroidogenesis (EATS) pathways of Japanese medaka. From these chemicals, 14 compounds, namely, 17β-estradiol (E2), ethinylestradiol (EE2), tamoxifen (TAM), 11-ketotestosterone (11-KT), 17β-trenbolone (TRB), flutamide (FLU), vinclozolin (VIN), triiodothyronine (T3), perfluorooctanoic acid (PFOA), tetrabromobisphenol A (TBBPA), terephthalic acid (TPA), trifloxystrobin (TRF), ketoconazole (KTC), and prochloraz (PCZ), were selected as references and used for the identification of apical endpoints within the EATS modalities. Among these endpoints, during classification, priorities are given to sex reversal (masculinization of females and feminization of males), gonad histology (testis-ova or ovotestis), secondary sex characteristics (anal fin papillae of males), plasma and liver vitellogenin (VTG) contents in males, swim bladder inflation during larval development, hepatic vitellogenin (vtg) and choriogenin (chg) genes in the liver of males, and several genes, including estrogen-androgen-thyroid receptors in the hypothalamus-pituitary-gonad/thyroid axis (HPG/T). After reviewing 205 articles, we identified 108 (52.68%), 46 (22.43%), 19 (9.26%), 22 (17.18%), and 26 (12.68%) papers that represented studies on estrogen endocrine disruptors (EEDs), androgen endocrine disruptors (AEDs), thyroid endocrine disruptors (TEDs), and/or steroidogenesis modulators (MOS), respectively. Most importantly, among 128 EDCs, 32 (25%), 22 (17.18%), 15 (11.8%), and 14 (10.93%) chemicals were classified as EEDs, AEDs, TEDs, and MOS, respectively. We also identified 43 (33.59%) chemicals as high-priority candidates for tier 2 tests, and 13 chemicals (10.15%) show enough potential to be considered EDCs without any further tier-based studies. Although our literature search was unable to identify the EATS targets of 45 chemicals (35%) studied in 60 (29.26%) of the 205 articles, our approach has sufficient potential to further move the laboratory-based research data on Japanese medaka for applications in regulatory risk assessments in humans.

Environmental occurrence and ecotoxicity of aquaculture-derived plastic leachates

Plastic products such as fishing nets and foam buoys have been widely used in aquaculture. To enhance the desirable characteristics of the final equipment, plastic gear for aquaculture is mixed with a wide range of additives. Recent studies have shown that additives could be leached out to the environment with a long-term use of aquaculture plastics, forming aquaculture-derived plastic leachates. It should be emphasized that some leachates such as phthalic acid esters (PAEs) and organophosphate esters (OPEs) are endocrine disruptors, which could increase the exposure risk of aquatic products and subsequently display potential threats to human health via food chain. However, systematic studies on the release, occurrence, bioaccumulation, and toxic effects of aquaculture-derived plastic leachates are missing, overlooking their potential sources and ecotoxicological risks in aquatic environments. We have reviewed and compared the concentrations of major plastic leachates in the water environment and organisms of global aquaculture and non-farmed areas, confirming that aquaculture leachate is an important source of contaminants in the environment. Moreover, the toxic effects of aquaculture-derived plastic additives and the related mechanisms are summarized with fish as a representative, revealing their potential health risk. In addition, we proposed current challenges and future research needs, which provides scientific guidance for the use and management of plastic products in aquaculture industries.

Long-term exposure to bisphenol A and its analogues alters the behavior of marine medaka (Oryzias melastigma) and causes hepatic injury

Bisphenols (BPA, BPF, and BPAF) are widely present in the aquatic environment and have various adverse effects on aquatic organisms. However, their hepatic toxicity in marine fish is not fully understood. Hence, we examined the growth parameters, histological features, antioxidant defense mechanisms, and gene expression profiles in the livers of marine medaka after exposure to single and combined bisphenols for 70 days. The final body weight and final body length of males exposed to BPAF were significantly higher than those in the control group, and the survival rate was significantly lower. Bisphenol exposure led to vacuolization and local lesions in the liver, especially in the BPAF group, and altered antioxidant enzyme activity in the liver, leading to oxidative stress. In addition, after bisphenol exposure, marine medaka showed anxiolytic effects and a significant reduction in swimming distance compared with that in the control group. As determined by RNA-seq, bisphenol exposure altered multiple biological pathways in the liver, such as fatty acid biosynthesis, fatty acid metabolism, and ribosome biogenesis pathways, with significant changes in gene expression levels. In particular, chgs and vtgs were significantly up-regulated after BPAF exposure, suggesting an estrogenic effect. Overall, bisphenols can adversely affect the growth and metabolism of marine medaka. BPF and BPAF may not be ideal substitutes for BPA.

Summary of 17 chemicals evaluated by OECD TG229 using Japanese Medaka, Oryzias latipes in EXTEND 2016

In June 2016, the Ministry of the Environment of Japan announced a program "EXTEND2016" on the implementation of testing and assessment for endocrine active chemicals, consisting of a two-tiered strategy. The aim of the Tier 1 screening and the Tier 2 testing is to identify the impacts on the endocrine system and to characterize the adverse effects to aquatic animals by endocrine disrupting chemicals detected in the aquatic environment in Japan. For the consistent assessment of the effects on reproduction associated with estrogenic, anti-estrogenic, androgenic, and/or anti-androgenic activities of chemicals throughout Tier 1 screening to Tier 2 testing, a unified test species, Japanese medaka (Oryzias latipes), has been used. For Tier 1 screening, the in vivo Fish Short-Term Reproduction Assay (OECD test guideline No. 229) was conducted for 17 chemicals that were nominated based on the results of environmental monitoring, existing knowledge obtained from a literature survey, and positive results in reporter gene assays using the estrogen receptor of Japanese medaka. In the 17 assays using Japanese medaka, adverse effects on reproduction (i.e., reduction in fecundity and/or fertility) were suggested for 10 chemicals, and a significant increase of hepatic vitellogenin in males, indicating estrogenic (estrogen receptor agonistic) potency, was found for eight chemicals at the concentrations in which no overt toxicity was observed. Based on these results, and the frequency and the concentrations detected in the Japanese environment, estrone, 4-nonylphenol (branched isomers), 4-tert-octylphenol, triphenyl phosphate, and bisphenol A were considered as high priority candidate substances for the Tier 2 testing.

Structural analysis and characterization of egg-envelope in the Indian freshwater murrel, Channa punctatus

Egg-envelope, an acellular coat, surrounds the egg and is essential for vitellogenin incorporation. It also plays a pivotal role during fertilization and provides protection to the developing embryo. In the present study, scanning electron microscopy was used to elucidate the structural details of isolated egg-envelopes from the Indian freshwater murrel, Channa punctatus. Several pores and single micropyle were observed on outer surface, whereas inner layer indicated deposition of proteinaceous material. The constituent proteins of egg-envelope were further characterized by Fourier transform infrared (FT-IR) spectroscopy, and electrophoresis and mass-spectrometry (MALDI-TOF-MS/MS). The secondary structure of egg-envelope proteins showed the presence of antiparallel ß-pleated sheets and aromatic amino acids. These proteins resolved into two peptides (130 kDa and 68 kDa) under denaturing conditions, which exhibited glycoprotein nature. The peptide band with low molecular mass showed significant similarity with transmembrane protein, whereas peptide band with high molecular mass matched with choriogenin protein of other fishes. These results confirm that chorion is derived from precursor protein, Choriogenin, in murrel. Chemical composition of egg-envelope supports that chorion is responsible exchange material and chemical defence during embryogenesis.

Genotoxic biomarkers and histological changes in marine medaka (Oryzias melastigma) exposed to 17α-ethynylestradiol and 17β-trenbolone

Endocrine-disrupting pollutants in marine environments have aroused great concern for their adverse effects on the reproduction of marine organisms. This study aimed to seek promising biomarkers for estrogenic/androgenic chemicals. First, two possible male-specific genes, SRY-box containing gene 9a2 (sox9a2) and gonadal soma-derived factor (gsdf), were cloned from marine medaka (Oryzias melastigma). Then the responses of sox9a2, gsdf, choriogenin (chgH and chgL), vitellogenin (vtg1 and vtg2), and cytochrome P450 aromatase (cyp19a and cyp19b) were investigated after exposure to 17α-ethynylestradiol (EE₂) and 17β-trenbolone (TB) at 2, 10, and 50 ng/L. The results showed that gsdf was specifically expressed in the testes and easily induced in the ovaries after TB exposure, indicating that gsdf was a potential biomarker of environmental androgens. ChgL was a useful biomarker of weak estrogen pollution for its high sensitivity to low levels of EE₂. In addition, both EE₂ and TB exposure damaged gonadal structures and inhibited gonadal development.

Expression of zona pellucida 3 gene is regulated by 17α-ethinylestradiol in adult topmouth culter Culter alburnus

Estrogen could lead to abnormal modulation or disruption of physical development, reproduction and sexual behavior in aquatic wildlife, especially in fish. Information on the toxicity of estrogens to native species in that can be used in site-specific risk assessments is scarce. In the present study, one zona pellucida 3 (ZP3) homologue termed CaZP3 was firstly identified from topmouth culter Culter alburnus, following its structural characteristics, tissue distribution and transcriptional modulation to 17α-ethinylestradiol (EE2) exposure were investigated. Meanwhile, vitellogenin (VTG) gene was employed to provide a comparison of the reactive ability to EE2 induction. The CaZP3 characterized with analogical functional domains such as ZP domain, SP, IHP, EHP, 12 cysteine residues, one N-linked glycosylation site and two conserved O-linked glycosylation sites and equal number of eight exons and seven introns with ZP3 counterparts of higher species. CaZP3 mRNA predominantly expressed in ovary, besides, highly expressed in female heart and male muscle and relatively high expressed in testis. CaZP3 has the lower reactive ability to EE2 induction in comparison with VTG, however, CaZP3 transcripts were significantly induced in gonads of both male and female culter by EE2 and could be used as an alternative biomarker to monitor EE2 activity. The present results supplement the database for toxicity of EE2, especially for fish species endemic to China and provide some useful information for the monitoring of EE2 activity in aquatic environment.

Returning to normal? Assessing transcriptome recovery over time in male rainbow darter (Etheostoma caeruleum) liver in response to wastewater-treatment plant upgrades

The present study measured hepatic transcriptome responses in male rainbow darter (Etheostoma caeruleum) exposed to 2 municipal wastewater-treatment plants (MWWTPs; Kitchener and Waterloo) over 4 fall seasons (2011-2014) in the Grand River (Ontario, Canada). The overall goal was to determine if upgrades at the Kitchener MWWTP (in 2012) resulted in transcriptome responses indicative of improved effluent quality. The number of differentially expressed probes in fish downstream of the Kitchener outfall (904-1223) remained comparable to that downstream of Waterloo (767-3867). Noteworthy was that year and the interaction of year and site explained variability in more than twice the number of transcripts than site alone, suggesting that year and the interaction of year and site had a greater effect on the transcriptome than site alone. Gene set enrichment analysis revealed a gradual reduction in the number of gene ontologies over time at exposure sites, which corresponded with lower contaminant load. Subnetwork enrichment analysis revealed that there were noticeable shifts in the cell pathways differently expressed in the liver preupgrade and postupgrade. The dominant pathways altered preupgrade were related to genetic modifications and cell division, whereas postupgrade they were associated with the immune system, reproduction, and biochemical responses. Molecular pathways were dynamic over time, and following the upgrades, there was little evidence that gene expression profiles in fish collected from high-impact sites postupgrade were more similar to those in fish collected from reference site. Environ Toxicol Chem 2017;36:2108-2122. © 2017 SETAC.

How Does Reference Site Selection Influence Interpretation of Omics Data?: Evaluating Liver Transcriptome Responses in Male Rainbow Darter (Etheostoma caeruleum) across an Urban Environment

Studies quantifying the influence of reference site selection on transcriptomic profiles in aquatic organisms exposed to complex mixtures are lacking in the literature, despite the significant implications of such research for the interpretation of omics data sets. We measured hepatic transcriptomic responses in fish across an urban environment in the central Grand River watershed (Ontario, Canada). Adult male rainbow darter (RBD) (Etheostoma caeruleum) were collected from nine sites at varying distances from two major municipal wastewater treatment plants (MWWTPs) (Waterloo, Kitchener), including three upstream reference sites. The transcriptomic response in RBD was independently compared with that of fish from each of the three reference sites. Data collected in fish downstream of the Waterloo MWWTP (poorest effluent quality) suggested that ∼15.5% of the transcriptome response was influenced by reference site selection. In contrast, at sites where the impact of MWWTPs was less-pronounced and fish showed less of a transcriptome response, reference site selection had a greater influence (i.e., ∼56.9% of transcripts were different depending on the site used). This study highlights the importance of conducting transcriptomics studies that leverage more than one reference site, and it broadens our understanding of the molecular responses in fish in dynamic natural environments.

Temporal patterns of induction and recovery of biomarker transcriptional responses to 4-Nonylphenol and 17β-estradiol in the estuarine arrow goby, Clevelandia ios

Several estuaries along the Pacific Ocean coast of North America were identified recently as having elevated 4-nonylphenol (4-NP) in sediments and biota, raising concerns about reproductive impacts for wildlife given 4-NP's established estrogenic activity as an endocrine-disrupting compound. Here we characterize 4-NP mediated induction and recovery of estrogen-sensitive gene transcripts in the arrow goby (Clevelandia ios), an intertidal fish abundant in estuarine mud flats on the west coast of North America. Male gobies were exposed to waterborne 4-NP at 10 μg/L or 100 μg/L for 20 days followed by a 20 day depuration period. Additional males were treated with 17β-estradiol (E2; 50 ng/L). 4-NP at 100 μg/L elevated hepatic mRNAs encoding vitellogenins A (vtgA) and C (vtgC) and choriogenin L (chgL) within 72 h, and choriogenin H minor (chgHm) within 12 days. Hepatic mRNAs encoding estrogen receptor alpha (esr1) were also elevated after 12 days of 4-NP exposure, but returned to pre-exposure levels at 20 days even under continuing 4-NP treatment. 4-NP did not alter mRNA levels of estrogen receptor gamma (esr2a) in the liver, or of esr1, esr2a, and cytochrome P450 aromatase B (cyp19a1b) in the brain. The temporal pattern of initial induction for hepatic vtgA, vtgC, and chgL transcripts by 4-NP mirrored the pattern by E2, while chgHm and esr1 mRNA induction by 4-NP lagged 2-11 days behind the responses of these transcripts to E2. These findings establish 4-NP concentration- and time-dependent induction patterns of choriogenin and vitellogenin transcription following exposure to environmentally relevant 4-NP concentrations, while concurrently demonstrating tissue-specific induction patterns for esr1 by estrogenic compounds. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1513-1529, 2017.

The potential immune modulatory effect of chronic bisphenol A exposure on gene regulation in male medaka (Oryzias latipes) liver

Bisphenol A (BPA) is a well-known estrogenic endocrine disrupting chemical (EDC) ubiquitously present in various environmental media. The present study aims to identify the responsive genes in male fish chronically exposed to low concentrations of BPA at the transcription level. We screened genes from a suppression subtractive hybridization library constructed from male medaka (Oryzias latipes) livers after 60-d exposure to 10μg/L BPA under the condition at which changes of hepatic antioxidant parameters have been previously reported. The identified genes were predicted to be involved in multiple biological processes including antioxidant physiology, endocrine system, detoxification, notably associated with the immune response processes. With real time PCR analysis, the immune-associated genes including hepcidin-like precursor, complement component and factors, MHC class I, alpha-2-macroglobulin and novel immune-type receptor 6 isoform were significantly up-regulated in a nonmonotonic dose response pattern in livers upon exposure to different concentrations of BPA (0.1, 1, 10, 100, 1000μg/L). Our results demonstrated a negative impact on gene regulation in fish chronically exposed to relatively low and environmentally relevant concentrations of BPA, and suggested the potential immune modulatory effect of chronic EDC exposure on fish. The immunotoxicity of BPA and other EDCs should be much concerned for the health of human beings and other vertebrates exposed to it.

Comprehensive transcriptomic analysis of the process of gonadal sex differentiation in the turbot (Scophthalmus maximus)

The turbot is a flatfish with a ZW/ZZ sex determination system but with a still unknown sex determining gene(s), and with a marked sexual growth dimorphism in favor of females. To better understand sexual development in turbot we sampled young turbot encompassing the whole process of gonadal differentiation and conducted a comprehensive transcriptomic study on its sex differentiation using a validated custom oligomicroarray. Also, the expression profiles of 18 canonical reproduction-related genes were studied along gonad development. The expression levels of gonadal aromatase cyp19a1a alone at three months of age allowed the accurate and early identification of sex before the first signs of histological differentiation. A total of 56 differentially expressed genes (DEG) that had not previously been related to sex differentiation in fish were identified within the first three months of age, of which 44 were associated with ovarian differentiation (e.g., cd98, gpd1 and cry2), and 12 with testicular differentiation (e.g., ace, capn8 and nxph1). To identify putative sex determining genes, ∼4.000 DEG in juvenile gonads were mapped and their positions compared with that of previously identified sex- and growth-related quantitative trait loci (QTL). Although no genes mapped to the previously identified sex-related QTLs, two genes (foxl2 and 17βhsd) of the canonical reproduction-related genes mapped to growth-QTLs in linkage group (LG) 15 and LG6, respectively, suggesting that these genes are related to the growth dimorphism in this species.

Background fish feminization effects in European remote sites

Human activity has spread trace amounts of chemically stable endocrine-disrupting pollutants throughout the biosphere. These compounds have generated a background level of estrogenic activity that needs to be assessed. Fish are adequate sentinels for feminization effects as male specimens are more sensitive than humans to exogenous estrogenic compounds. High mountain lakes, the most distant environments of continental areas, only receive semi-volatile compounds from atmospheric deposition. We analyzed the expression levels of estrogen-regulated genes in male fish from these mountain lakes in Europe. Incipient feminization involving expression of estrogen receptor and zona radiata genes revealed a widespread diffuse estrogenic impact. This effect was correlated with the concentrations of some organochlorine compounds in fish and was consistent with the persistent occurrence of these tropospheric pollutants in the most remote planet regions. These results should be of general concern given the increasing endocrine disruption effects in human populations.

Chronic exposure of killifish to a highly polluted environment desensitizes estrogen-responsive reproductive and biomarker genes

Reproductive and endocrine disruption is commonly reported in aquatic species exposed to complex contaminant mixtures. We previously reported that Atlantic killifish (Fundulus heteroclitus) from the chronically contaminated Newark Bay, NJ, exhibit multiple endocrine disrupting effects, including inhibition of vitellogenesis (yolk protein synthesis) in females and false negative vitellogenin biomarker responses in males. Here, we characterized the effects on estrogen signaling and the transcriptional regulation of estrogen-responsive genes in this model population. First, a dose-response study tested the hypothesis that reproductive biomarkers (vtg1, vtg2, chg H, chg Hm, chg L) in Newark Bay killifish are relatively less sensitive to 17β-estradiol at the transcriptional level, relative to a reference (Tuckerton, NJ) population. The second study assessed expression for various metabolism (cyp1a, cyp3a30, mdr) and estrogen receptor (ER α, ER βa, ER βb) genes under basal and estrogen treatment conditions in both populations. Hepatic metabolism of 17β-estradiol was also evaluated in vitro as an integrated endpoint for adverse effects on metabolism. In the third study, gene methylation was evaluated for promoters of vtg1 (8 CpGs) and vtg2 (10 CpGs) in both populations, and vtg1 promoter sequences were examined for single nucleotide polymorphism (SNPs). Overall, these studies show that multi-chemical exposures at Newark Bay have desensitized all reproductive biomarkers tested to estrogen. For example, at 10ng/g 17β-estradiol, inhibition of gene induction ranged from 62% to 97% for all genes tested in the Newark Bay population, relative to induction levels in the reference population. The basis for this recalcitrant phenotype could not be explained by a change in 17β-estradiol metabolism, nuclear estrogen receptor expression, promoter methylation (gene silencing) or SNPs, all of which were unaltered and normal in the Newark Bay population. The decreased transcriptional sensitivity of estrogen-responsive genes is suggestive of a broad effect on estrogen receptor pathway signaling, and provides insight into the mechanisms of the endocrine disrupting effects in the Newark Bay population.

Reproductive biomarkers responses induced by xenoestrogens in the characid fish Astyanax fasciatus inhabiting a South American reservoir: an integrated field and laboratory approach

Field studies evaluating the effects of endocrine disruption chemicals (EDCs) on the fish reproduction are scarce worldwide. The goal of this study was to assess hepatic levels of vitellogenin (Vtg), zona radiata proteins (Zrp) and insulin-like growth factors (IGF-I and IGF-II), and relating them to reproductive endpoints in a wild fish population habiting a reservoir that receive domestic sewage, agricultural and industrial residues. Adult fish Astyanax fasciatus were sampled during the reproductive season in five sites from the Furnas Reservoir, Grande River, and Paraguay-Paraná basin. As a control to field data, fish were experimentally exposed via dietary intake, to oestradiol benzoate (OB) for 7 days. Fish from site with little anthropogenic interference showed hepatic levels of Vtg, Zrp and IGF-I and IGF-II similar to those from the non-treated experimental group. In sites located immediately downstream from the municipal wastewater discharges, the water total oestrogen was >120 ng/l, and male fish displayed increased Vtg and Zrp and decreased IGF-I levels similar to OB treated fish. In females, levels of Vtg, Zrp, IGF-I and IGF-II suggest an impairment of final oocyte maturation and spawning, as also detected by frequency of over-ripening, follicular atresia and fecundity. At the sites that receive agricultural and industrial residues, the water total oestrogen was <50 ng/l and females showed decreased Zrp and increased IGF-II levels associated to reduced diameter of vitellogenic follicles, indicating an inhibition of oocyte growth. Overall, the current study reports oestrogenic contamination impairing the reproduction of a wild fish from a hydroeletric reservoir and, the data contribute to improving the current knowledge on relationship between hepatic Vtg, Zrp and IGF-I and IGF-II, and reproductive endpoints in a teleost fish. In addition, our data point out novel reproductive biomarkers (IGF-I, IGF-II and over-ripening) to assessing xenoestrogenic contamination in freshwater ecosystems.

Expression of two zona pellucida genes is regulated by 17α-ethinylestradiol in adult rare minnow Gobiocypris rarus

Zona pellucida (ZP) proteins are glycoproteins synthesized in liver, ovary or in both tissues in fish. In the present study, we aimed to determine the responsiveness of ZP2 and ZP3 to 17α-ethinylestradiol (EE2) in adult rare minnow Gobiocypris rarus. The full length of ZP3 cDNA was firstly characterized and its tissue distribution revealed that ZP3 mRNA was predominantly expressed in ovary of G. rarus. The gene expression profiles of ZP2, ZP3 and vitellogenin (VTG) were analyzed in gonad and liver of adult G. rarus exposed to EE2 at 1, 5, 25, and 125 ng/L for 3 and 6 days. The results show that ZP2 is more sensitive than ZP3 in gonads of both genders, and VTG in liver is extremely sensitive to EE2 in male fish. However, at lower concentrations (1 and 5 ng/L), the ZP2 in testes shows higher responsiveness to EE2 compared with VTG in rare minnow. The 5' flanking regions of ZP2 and ZP3 were isolated and the comparison of transcription factors in the regions of ZP2 and ZP3 suggested that the disparity for the responsiveness of ZP2 and ZP3 to EE2 could partly be a result of differential cis-elements such as oocyte-specific protein (Osp1) binding sites or/and sex-determining region Y (SRY) binding site.

Biomarker gene response in male Medaka (Oryzias latipes) chronically exposed to silver nanoparticle

The chronic toxicity test has been conducted for twenty-eight days to characterize the hepatic expression levels of eight stress-related genes after exposing Medaka to two doses of silver nitrate or a silver nanoparticle (Ag-NP) using real time RT-PCR analysis. This extends our previously published work to include three additional biomarkers and three later time points. In comparing with the control, the significant induction of MT and GST genes in livers of the fish exposed to 1 μg/l Ag-NPs was observed at various time points during the test period. The Orla C3-1 (Medaka) gene was slightly induced only with 1 μg/l Ag-NPs at 7-day exposure while the suppression of p53 and HSP70 was recorded in all exposures at the end of the test. The gene encoding transferrin was repressed at day 21 by both silver types and at every exposure dosage. These results revealed that the Ag-NPs increase metal detoxification, oxidative and inflammatory stress, and finally stimulate immune responses in Medaka. The conspicuous induction of choriogenin L and vitellogenin 1 in male fish exposed to Ag-NPs, especially at 7- and 21-day, compared with the exposures of AgNO(3) or control was the first attempt to examine estrogenic effects of Ag-NPs.

Expression of zona pellucida B proteins in juvenile rare minnow (Gobiocypris rarus) exposed to 17α-ethinylestradiol, 4-nonylphenol and bisphenol A

Zona pellucida (ZP) containing proteins are glycoproteins in teleost chorion and are encoded by several gene subfamilies, mainly including ZPA, ZPB, ZPC and ZPX genes. In teleost species, ZP genes are expressed either in liver under regulation of estrogen or in ovary. In the present study, five ZP gene isoforms were isolated and characterized in Gobiocypris rarus. The putative amino acid sequences of these ZP gene isoforms contain the typical trefoil motif and a ZP domain. These five G. rarus ZP gene isoforms were named as grZPB.1, grZPB.2, grZPB.3, grZPB.4 and grZPB.5. Real-time quantitative reverse transcription PCR (RT-qPCR) analysis indicated that all these ZP mRNA isoforms were exclusively expressed in ovary. G. rarus juveniles at the age of 21 days postfertilization were exposed to 17α-ethinylestradiol (EE2; 0.01, 0.1 and 1 nM), 4-nonylphenol (4-NP; 10, 100 and 1000 nM) or bisphenol A (BPA; 0.1, 1 and 10nM) for 3 days. mRNA expressions of ZPB isoforms following the exposure to xenoestrogen were detected by RT-qPCR. Data were analyzed by the 2(-△△Cq) method. The results indicate that induction by 0.1-1nM EE2 on mRNA expression of the grZPB isoforms is weaker than for vitellogenin. 4-NP exposures at three concentrations had differential effects on the grZPBs. BPA at three concentrations weakly induced mRNA expression of the grZPB isoforms.

Early expression of zona pellucida proteins under octylphenol exposure in Cichlasoma dimerus (Perciformes, Cichlidae)

An increasing number of widely used industrial and agricultural chemicals are being found to cause endocrine disruption. In fishes, xenoestrogens can induce female proteins, and in some cases, the development of testis-ova, demonstrating feminization of males. In this study we analyzed the effect of an acute exposure of adult male Cichlasoma dimerus fish to estradiol (E(2)) and octylphenol (OP). E(2) and OP were injected at 10 and 50 μg/g body weight doses, respectively. After a single OP dose, liver was processed for RNA extraction at 1, 3, 12, 24, and 72 h. PCR was performed using cDNA and primers for egg coat or zona pellucida proteins (ZP). Genes encoding ZPB and ZPC isoforms were sequenced. E(2)-induced fish were sacrificed at 72 h. Using multiple OP or E(2) injections, blood and surface mucus were sampled on days 0, 3, 6, 9, and 13. On day 13 fish were sacrificed for liver and testis dissection. Histological examination of E(2) and OP-treated fish livers showed cellular disarray and intense cytoplasmatic basophilia within hepatocytes, probably due to increased mRNA synthesis, as well as hypertrophied euchromatic nuclei, and conspicuous nucleoli, indicative of augmented cell activity. An abnormal amount of sperm and immature germ cells within the testis lumen were seen in treated fish, suggesting reproductive impairment. Both plasma and mucus revealed the presence of ZP (and vitellogenin) at day 3 and thereafter with E(2) treatment, using Western and Dot blot techniques; OP effects were delayed in time. These results validate the analysis of mucus by Dot blot as an easy and rapid technique to address endocrine disruption caused by OP. Quantitative gene expression showed induction of liver ZPB and ZPC upon OP injection; muscle, brain, and intestine did not express any ZP. Both ZPs were induced at 1h post injection, but only ZPB expression was statistically significant. At 12h, both ZPs increased significantly, reaching the same levels of E(2)-challenged males after 72 h. Therefore, OP mimicked the action of E(2) with a prompt and strong xenoestrogenic effect, evidenced by the early response through mRNA and protein expression of ZP and the concomitant histological liver and testis alterations.

Hepatic transcriptomic and metabolomic responses in the Stickleback (Gasterosteus aculeatus) exposed to ethinyl-estradiol

An established three-spined stickleback (Gasterosteus aculeatus) cDNA array was expanded to 14,496 probes with the addition of hepatic clones derived from subtractive and normalized libraries from control males and males exposed to model toxicants. Microarrays and one-dimensional (1)H nuclear magnetic resonance (NMR) spectroscopy, together with individual protein and gene biomarkers were employed to investigate the hepatic responses of the stickleback to ethinyl-estradiol (EE(2)) exposure. Male fish were exposed via the water to EE(2), including environmentally relevant concentrations (0.1-100ng/l) for 4 days, and hepatic transcript and metabolite profiles, kidney spiggin protein and serum vitellogenin concentrations were determined in comparison to controls. EE(2) exposure did not significantly affect spiggin concentration but significantly induced serum vitellogenin protein at the threshold concentration of 32ng/l. (1)H NMR coupled with robust univariate testing revealed only limited changes, but these did support the predicted modulation of the amino acid profile by transcriptomics. Transcriptional induction was found for hepatic vitellogenins and choriogenins as expected, together with a range of other EE(2)-responsive genes. Choriogenins showed the more sensitive responses with statistically significant induction at 10ng/l. Real-time polymerase chain reaction (PCR) confirmed transcriptional induction of these genes. Phosvitinless vitellogenin C transcripts were highly expressed and represent a major form of the egg yolk precursors, and this is in contrast to other fish species where it is a minor component of vitellogenic transcripts. Differences in inducibility between the vitellogenins and choriogenins appear to be in accordance with the sequential formation of chorion and yolk during oogenesis in fish.

Changes in gene expression profile of medaka with acute toxicity of Arochlor 1260, a polychlorinated biphenyl mixture

Differential gene expression profiling was performed with a cDNA microarray in the liver tissue of the medaka fish, Oryzias latipes, after exposure to Arochlor 1260, a polychlorinated biphenyl (PCB) mixture, which is used as a coolant and insulating fluid for transformers and capacitors and is classified as a persistent organic pollutant. Twenty-six differentially expressed candidate genes were identified. The expression of 12 genes was up-regulated and that of 14 genes was down-regulated. These genes are associated with the cytoskeleton, development, endocrine/reproduction, immunity, metabolism, nucleic acid/protein binding, and signal transduction, or are uncategorized. The transcription of molecular biomarkers known to be involved in endocrine disruption (e.g., vitellogenins, choriogenins, and estrogen receptor alpha) was highly up-regulated. The same tendencies in gene expression changes were observed with real-time quantitative PCR (qRT-PCR) analysis, which was conducted to examine 12 selected candidate genes. These genes could be used as molecular biomarkers for biological responses to toxic chemicals, especially endocrine disrupting and carcinogenic chemical contamination in aquatic environments.

Linking mechanistic and behavioral responses to sublethal esfenvalerate exposure in the endangered delta smelt; Hypomesus transpacificus (Fam. Osmeridae)

BACKGROUND

The delta smelt (Hypomesus transpacificus) is a pelagic fish species listed as endangered under both the USA Federal and Californian State Endangered Species Acts and considered an indicator of ecosystem health in its habitat range, which is limited to the Sacramento-San Joaquin estuary in California, USA. Anthropogenic contaminants are one of multiple stressors affecting this system, and among them, current-use insecticides are of major concern. Interrogative tools are required to successfully monitor effects of contaminants on the delta smelt, and to research potential causes of population decline in this species. We have created a microarray to investigate genome-wide effects of potentially causative stressors, and applied this tool to assess effects of the pyrethroid insecticide esfenvalerate on larval delta smelt. Selected genes were further investigated as molecular biomarkers using quantitative PCR analyses.

RESULTS

Exposure to esfenvalerate affected swimming behavior of larval delta smelt at concentrations as low as 0.0625 mug.L-1, and significant differences in expression were measured in genes involved in neuromuscular activity. Alterations in the expression of genes associated with immune responses, along with apoptosis, redox, osmotic stress, detoxification, and growth and development appear to have been invoked by esfenvalerate exposure. Swimming impairment correlated significantly with expression of aspartoacylase (ASPA), an enzyme involved in brain cell function and associated with numerous human diseases. Selected genes were investigated for their use as molecular biomarkers, and strong links were determined between measured downregulation in ASPA and observed behavioral responses in fish exposed to environmentally relevant pyrethroid concentrations.

CONCLUSIONS

The results of this study show that microarray technology is a useful approach in screening for, and generation of molecular biomarkers in endangered, non-model organisms, identifying specific genes that can be directly linked with sublethal toxicological endpoints; such as changes in expression levels of neuromuscular genes resulting in measurable swimming impairments. The developed microarrays were successfully applied on larval fish exposed to esfenvalerate, a known contaminant of the Sacramento-San Joaquin estuary, and has permitted the identification of specific biomarkers which could provide insight into the factors contributing to delta smelt population decline.

Endocrine disruptors modulate expression of hepatic choriogenin genes in the hermaphroditic fish, Kryptolebias marmoratus

Choriogenins (Chgs) are precursors of inner layer of egg envelope that are synthesized in fish liver in response to estrogens. Therefore, study of their expression serves as biomarker of exposure to endocrine disrupting chemicals (EDCs). The self-fertilizing fish, Kryptolebias marmoratus has been established as a model species for testing the action of EDCs. To use this fish as a model for assessing estrogenic activity of EDCs on Chg expression, two K. marmoratus choreogenin genes, Km-ChgH and Km-ChgL were cloned and their expression was analyzed in different tissues and in developmental stages by real-time RT-PCR. Expression levels of liver mRNA were compared between hermaphrodites and secondary males after exposure to EDCs. Km-ChgH and Km-ChgL genes that were predominantly expressed in liver contained zona pellucida (ZP) domains. During embryonic development, low expression of mRNA was observed at stage 1 (2 dpf) that reached highest level at stage 4 (12 dpf) or stage 5 (5 h post hatching). The expression of Km-Chg mRNAs was highly increased in liver exposed to natural estrogen, 17alpha-estradiol (E2) as well as EDCs such as bisphenol A and 4-n-nonylphenol in both the gender types. Another EDC, 4-tert-octylphenol, showed modulatory effect only on Km-ChgH in hermaphrodites. Tamoxifen, an antagonist of the estrogen receptor showed no effect on expression of Chg genes in either of the gender types of K. marmoratus. These findings indicate that Km-Chg genes would be associated with estrogen and measurement of their expression would serve as a surrogate biomarker of exposure to environmental EDCs.

A molecular biomarker for disruption of crustacean molting: the N-acetyl-beta-glucosaminidase mRNA in the epidermis of the fiddler crab

Several environmentally persistent chemicals have been found to be capable of disrupting crustacean molting. Considering the importance of molting in the life of crustaceans, there is a need to develop a molecular biomarker that can reflect the disrupting effects of contaminants on ecdysteroid signaling in crustaceans. N-acetyl-beta-glucosaminidase (NAG) is a chitinolytic enzyme found in crustacean epidermis. The results of the present investigation show that the transcription of NAG gene in the epidermis of the fiddler crab, Uca pugilator, is inducible by the molting hormone 20-hydroxyecdysone, which validates the use of NAG mRNA as a biomarker for molt-disrupting effects of xenobiotics.

Choriogenin and vitellogenin in red lip mullet (Chelon haematocheilus): purification, characterization, and evaluation as potential biomarkers for detecting estrogenic activity

Two vitelline envelope precursors (choriogenin H: Chg H; choriogenin L: Chg L) and an egg yolk precursor (vitellogenin B: VgB) were purified from red lip mullet. The mass of intact Chg H and Chg L were estimated to be approximately 215 kDa and approximately 69 kDa, respectively. In SDS-PAGE, Chg H and Chg L separated to positions corresponding to approximately 51 kDa and approximately 44 kDa, respectively. The mass of intact VgB was approximately 530 kDa and resolved into a polypeptide of approximately 185 kDa in SDS-PAGE. Specific antisera were raised against each purified protein and specific immunoassays were developed. When Chg H, Chg L and VgB were induced in the serum of immature mullet by injection with various doses of estradiol-17beta (E(2)), VgB exhibited the most sensitive response exhibiting high variation in its induced levels. The variation in induced levels of Chg H and L was relatively minimal although induction required higher doses of E(2) than with VgB. Serum samples obtained from immature mullet populations collected from their natural habitat exhibited similar profiles in the levels of these proteins. The present study suggests that the utilization of multiple biomarkers holds great importance for the reliable and accurate evaluation of estrogenic activity in aquatic environments.

Bisphenol A in the Aquatic Environment and Its Endocrine-Disruptive Effects on Aquatic Organisms

Bisphenol A [BPA; 2,2-bis(4-hydroxyphenyl)propane], which is mainly used in the production of epoxy resins and polycarbonate plastics, is a known endocrine disruptor and is acutely toxic to aquatic organisms. Due to intensified usage of these products, exposure of organisms to BPA via several routes, such as the environment and food, has increased. The aquatic environment is an important area for the study of BPA. This report reviews the literature concerning contamination routes and degradation of BPA in the aquatic environment and its endocrine-disruptive effects on aquatic organisms.

Choriogenin mRNA as a sensitive molecular biomarker for estrogenic chemicals in developing brackish medaka (Oryzias melastigma)

Teleost choriogenins, precursors of the inner layer subunits of the egg envelope, are regarded as sensitive biomarkers for estrogenic pollutants. In this study, two full-length cDNAs, omChgH and omChgL, which encode the choriogenin H and L forms, respectively, were isolated from a brackish medaka, Oryzias melastigma. 17beta-Estradiol (E2; 10 microg/L)-dependent expression of omChgH and omChgL was observed starting at embryonic stage 34 and restricted exclusively to the liver. In hatchlings, E2 induction of omChgH was stronger than that of omChgL. Static exposure of adult fish to E2 (0, 1, 10, 100, and 500 ng/L), 17alpha-ethinylestradiol (EE2; 0, 1, 10, 100 and 500 ng/L), 4-nonylphenol (NP; 0, 1, 10, 100, and 200 microg/L), and bisphenol A (BPA; 0, 1, 10, 100, and 200 microg/L) in artificial seawater for 7 days resulted in dose-dependent induction of both genes in the liver. In the male livers, the sensitivity of omChgH to these estrogenic compounds was higher than that of omChgL; the lowest-observed-effect concentrations (LOECs) of E2, EE2, NP, and BPA on omChgH were 10 ng/L, 10 ng/L, 100 microg/L and 100 microg/L, respectively, and on omChgL were 100 ng/L, 100 ng/L, 100 microg/L, and 200 microg/L, respectively. All these suggest that omChgH can be used as a highly sensitive biomarker for monitoring estrogenic chemicals in the marine environment.

Detection of environmental estrogenicity using transgenic medaka hatchlings (Oryzias latipes) expressing the GFP-tagged choriogenin L gene

The discharge of environmental estrogenic substances into the environment has an adverse effect on human and wildlife, especially aquatic organisms. Therefore, a simple, practical and sensitive method of detecting environmental estrogenicity is required. Previously, we established a transgenic medaka (Oryzias latipes) strain harboring choriogenin L (ChgL) tagged with green fluorescence protein (GFP), which is expressed in the liver in response to estrogen (E2). This strain of medaka could be a very useful tool in detecting aquatic estrogenicity. The appropriate conditions for analysis of estrogenicity were determined at various E2 concentrations, exposure periods and the developmental stages of medaka hatchlings. Furthermore, the relationship between E2 concentrations and GFP fluorescence intensity was investigated. It was found that fluorescence intensity of GFP depends largely on E2 concentration, exposure time and developmental stage. Hatchling at 4-day post-hatch (DPH) showed optimum conditions for exposure to E2 with optimum GFP intensity at 9 DPH. Additionally, the exposure period was optimized so that exposure from 4 DPH for 5 days showed a significant change in GFP intensity. E2 concentrations of 0, 12.5, 25, 50 and 100 ng/L were used, with 25 ng/L showing a clear increase in GFP intensity at day 6 of exposure. The sensitivity of vitellogenin (Vtg) induction was also examined by Western blot and enzyme-linked immunosorbent assay (ELISA) using whole-body homogenates of E2-exposed (0, 12.5, 25, 50 and 100 ng/L) juvenile medaka. Vitellogenin induction, as determined by Western blot, was found in those juveniles exposed to E2 at a concentration of 100 ng/L. Whereas, Vtg induction was detected by ELISA from juveniles exposed to 12.5 ng/L of E2. The results suggest that ChgL-GFP transgenic medaka could be a simple and practical tool in detecting environmental estrogenicity considering the actual concentrations of estrogenic activity in contaminated and/or wastewater.

Identification of potential biomarkers for diazinon exposure to Japanese Medaka (Oryzias latipes) using annealing control primers

A new differential display-polymerase chain reaction (PCR) method based on annealing control primers was used to screen and identify potential biomarkers from differentially expressed genes (DEGs) in medaka exposed to sub-lethal concentration of diazinon (100 ppb). Among the differentially expressed genes identified, the majority were in functional categories of protein biosynthesis, transport and metabolism according to the gene ontology classification. The differential expression of ribosomal protein genes was quantified by real time PCR. The genes encoding ribosomal proteins including L3 and S17 were selected as potential biomarkers for diazinon exposure in medaka fish.

Appropriate 'housekeeping' genes for use in expression profiling the effects of environmental estrogens in fish

Background

Attempts to develop a mechanistic understanding of the effects of environmental estrogens on fish are increasingly conducted at the level of gene expression. Appropriate application of real-time PCR in such studies requires the use of a stably expressed 'housekeeping' gene as an internal control to normalize for differences in the amount of starting template between samples.

Results

We sought to identify appropriate genes for use as internal controls in experimental treatments with estrogen by analyzing the expression of eight functionally distinct 'housekeeping' genes (18S ribosomal RNA [18S rRNA], ribosomal protein l8 [rpl8], elongation factor 1 alpha [ef1a], glucose-6-phosphate dehydrogenase [g6pd], beta actin [bactin], glyceraldehyde-3-phosphate dehydrogenase [gapdh], hypoxanthine phosphoribosyltransferase 1 [hprt1], and tata box binding protein [tbp]) following exposure to the environmental estrogen, 17α-ethinylestradiol (EE₂), in the fathead minnow (Pimephales promelas). Exposure to 10 ng/L EE₂ for 21 days down-regulated the expression of ef1a, g6pd, bactin and gapdh in the liver, and bactin and gapdh in the gonad. Some of these effects were gender-specific, with bactin in the liver and gapdh in the gonad down-regulated by EE₂ in males only. Furthermore, when ef1a, g6pd, bactin or gapdh were used for normalization, the hepatic expression of two genes of interest, vitellogenin (vtg) and cytochrome P450 1A (cyp1a) following exposure to EE₂ was overestimated.

Conclusion

Based on the data presented, we recommend 18S rRNA, rpl8, hprt1 and/or tbp, but not ef1a, g6pd, bactin and/or gapdh, as likely appropriate internal controls in real-time PCR studies of estrogens effects in fish. Our studies show that pre-validation of control genes considering the scope and nature of the experiments to be performed, including both gender and tissue type, is critical for accurate assessments of the effects of environmental estrogens on gene expression in fish.

Expression analysis of sex-specific and 17beta-estradiol-responsive genes in the Japanese medaka, Oryzias latipes, using oligonucleotide microarrays

Gene profiling of Japanese medaka (Oryzias latipes) was performed using an oligonucleotide DNA microarray representing 22,587 TIGR O. latipes gene indices (OLGIs). The average correlation coefficients for gene expression between individual mature fish were high (>0.95) for both female and male, indicating that the physiological status of medaka is highly reproducible under prescribed growth conditions. Of the 22,587 OLGIs, 2575 showed significant differences in expression between female and male. Exposure to 17beta-estradiol (E2) revealed 381 E2-responsive OLGIs in male medaka. Feminization and male-dysfunction factors of the E2-treated males calculated using the combination of Pearson correlation coefficient and Euclidean distances indicate that E2 treatment "weakly feminized" male medaka, while male physiological functions were not significantly disrupted. This study demonstrates the possibility of using medaka microarrays to estimate the overall effects of hormonally active chemicals.

Induction of hepatic choriogenin mRNA expression in male marine medaka: a highly sensitive biomarker for environmental estrogens

Teleost choriogenins, precursors of the inner layer subunits of egg envelope, have been recently introduced as sensitive biomarkers for exposure to estrogenic compounds. In this study, two full-length cDNAs-ojChgH and ojChgL which encode the choriogenin H and L forms, respectively, were cloned from the marine medaka, Oryzias javanicus. The deduced protein sequences of ojChgH and ojChgL are highly similar to the corresponding homologues in the freshwater medaka (O. latipes) with identities of 77.2 and 87.6%, respectively. Phylogenetic analysis indicated that ojChgH and ojChgL are members of two different classes of liver-specific ZP-domain containing proteins (ZPB and ZPC, respectively). Computer analysis of ca. 2 kb of the 5'-flanking sequences of ojChgH and ojChgL revealed that both genes contain a number of putative estrogen response elements (EREs) and/or half-site EREs. In vivo mRNA expression patterns of the genes were examined by quantitative real-time RT-PCR. ojChgH is expressed exclusively in the liver while ojChgL is co-expressed in the liver (major) and ovary (minor). Exposure of fish to waterborne 17beta-estradiol (E2) at environmentally relevant concentrations (1, 5, 10 and 100 ng/L) resulted in dose-dependent induction of both genes in the liver, with higher sensitivity and magnitude of induction in males than in females. In the male liver, induction of ojChgH is more sensitive to E2 than that of ojChgL and two other estrogen-responsive genes, estrogen receptor alpha (ojERalpha) and vitellogenin (ojVTG). The lowest-observed-effect concentration (LOEC) of E2 on induction of hepatic ojChgH mRNA is 1 ng/L. In the ovary, expression of ojChgL is non-responsive to E2 treatment. In conclusion, the present study suggested that induction of hepatic ojChgH mRNA in male fish may be a highly sensitive biomarker for exposure to environmental estrogens.

Screening and testing for endocrine disruption in fish-biomarkers as "signposts," not "traffic lights," in risk assessment

Biomarkers are currently best used as mechanistic "signposts" rather than as "traffic lights" in the environmental risk assessment of endocrine-disrupting chemicals (EDCs). In field studies, biomarkers of exposure [e.g., vitellogenin (VTG) induction in male fish] are powerful tools for tracking single substances and mixtures of concern. Biomarkers also provide linkage between field and laboratory data, thereby playing an important role in directing the need for and design of fish chronic tests for EDCs. It is the adverse effect end points (e.g., altered development, growth, and/or reproduction) from such tests that are most valuable for calculating adverseNOEC (no observed effect concentration) or adverseEC10 (effective concentration for a 10% response) and subsequently deriving predicted no effect concentrations (PNECs). With current uncertainties, biomarkerNOEC or biomarkerEC10 data should not be used in isolation to derive PNECs. In the future, however, there may be scope to increasingly use biomarker data in environmental decision making, if plausible linkages can be made across levels of organization such that adverse outcomes might be envisaged relative to biomarker responses. For biomarkers to fulfil their potential, they should be mechanistically relevant and reproducible (as measured by interlaboratory comparisons of the same protocol). VTG is a good example of such a biomarker in that it provides an insight to the mode of action (estrogenicity) that is vital to fish reproductive health. Interlaboratory reproducibility data for VTG are also encouraging; recent comparisons (using the same immunoassay protocol) have provided coefficients of variation (CVs) of 38-55% (comparable to published CVs of 19-58% for fish survival and growth end points used in regulatory test guidelines). While concern over environmental xenoestrogens has led to the evaluation of reproductive biomarkers in fish, it must be remembered that many substances act via diverse mechanisms of action such that the environmental risk assessment for EDCs is a broad and complex issue. Also, biomarkers such as secondary sexual characteristics, gonadosomatic indices, plasma steroids, and gonadal histology have significant potential for guiding interspecies assessments of EDCs and designing fish chronic tests. To strengthen the utility of EDC biomarkers in fish, we need to establish a historical control database (also considering natural variability) to help differentiate between statistically detectable versus biologically significant responses. In conclusion, as research continues to develop a range of useful EDC biomarkers, environmental decision-making needs to move forward, and it is proposed that the "biomarkers as signposts" approach is a pragmatic way forward in the current risk assessment of EDCs.

Effect of bisphenol A on maturation and quality of semen and eggs in the brown trout, Salmo trutta f. fario

In the present study male and female brown trout (Salmo trutta f. fario) were exposed to environmentally relevant concentrations of bisphenol A (1.75, 2.40, 5.00 microg l(-1)) during the late prespawning and spawning period and the effect of this contaminant on maturation, quantity and quality of semen and eggs was investigated. In males exposed to estimated BPA concentrations of 1.75 and 2.40 microg l(-1) semen quality was lower than in the control in the beginning of spawning (reduced sperm density, motility rate, and swimming velocity) and in the middle of spawning (reduced swimming velocity, at 2.40 microg l(-1) BPA also reduced sperm motility rate). Therefore, production of high quality semen was restricted to the end of the spawning season and delayed for approximately 4 weeks in comparison to the control. At BPA exposure levels of 5.00 microg l(-1) only one of eight males gave semen of low quality (reduced semen mass, motility rate, and swimming velocity). The percentage of ovulated females was similar for the control group and the groups exposed to estimated BPA concentrations of 1.75 and 2.40 microg l(-1), whereas at 5.00 microg l(-1) BPA females did not ovulate during the investigation. While brown trout of the control group ovulated between the 28 October and 12 November, brown trout exposed to estimated BPA concentrations of 1.75 microg l(-1) BPA ovulated approximately 2 weeks later and brown trout exposed to 2.40 microg l(-1) BPA approximately 3 weeks later. Therefore, the tested BPA concentrations affected the percentage of ovulated females and the time point of ovulation. No effect was observed on the quality of eggs (egg mass, percentile mass increase during hardening, egg fertility).

Annual changes in serum levels of two choriogenins and vitellogenin in masu salmon, Oncorhynchus masou

Annual changes in serum levels of two chorion precursors, choriogenin H (Chg H) and choriogenin L (Chg L), vitellogenin (Vg) and estradiol-17beta (E2) were quantified in masu salmon, Oncorhynchus masou, using specific immunoassays. Serum Chg levels were higher than Vg during the previtellogenic growth phase when circulating E2 levels were low ( approximately 0.1 ng/mL), suggesting higher sensitivity of Chg to E2. When oocyte growth shifted to the vitellogenic phase, Vg levels increased and became the most abundant in serum coincident with elevations of E2 and GSI. Chg H, Chg L and Vg peaked 1 month prior to ovulation at 0.61+/-0.08, 0.98+/-0.18 and 10.93+/-3.24 mg/mL, respectively. These results suggest that chorion formation by Chgs occurs prior to vitellogenesis and that the sensitivity of Chgs to low circulating E2 is closely related to the sequential events of oocyte growth.

Identification of choriogenin cis-regulatory elements and production of estrogen-inducible, liver-specific transgenic Medaka

Choriogenins (chg-H, chg-L) are precursor proteins of egg envelope of medaka and synthesized in the spawning female liver in response to estrogen. We linked a gene construct chg-L1.5 kb/GFP (a 1.5 kb 5'-upstream region of the chg-L gene fused with a green fluorescence protein (GFP) gene) to another construct emgb/RFP (a cis-regulatory region of embryonic globin gene fused with an RFP gene), injected the double fusion gene construct into 1- or 2-cell-stage embryos, and selected embryos expressing the RFP in erythroid cells. From the embryos, we established two lines of chg-L1.5 kb/GFP-emgb/RFP-transgenic medaka. The 3-month-old spawning females and estradiol-17beta (E2)-exposed males displayed the liver-specific GFP expression. The E2-dependent GFP expression was detected in the differentiating liver of the stage 37-38 embryos. In addition, RT-PCR and whole-mount in situ hybridization showed that the E2-dependent chg expression was found in the liver of the stage 34 embryos of wild medaka, suggesting that such E2-dependency is achieved shortly after differentiation of the liver. Analysis using serial deletion mutants fused with GFP showed that the region -426 to -284 of the chg-L gene or the region -364 to -265 of the chg-H gene had the ability to promote the E2-dependent liver-specific GFP expression of its downstream gene. Further analyses suggested that an estrogen response element (ERE) at -309, an ERE half-site at -330 and a binding site for C/EBP at -363 of the chg-L gene played important roles in its downstream chg-L gene expression. In addition, this transgenic medaka may be useful as one of the test animals for detecting environmental estrogenic steroids.

Differential gene expression analysis in fish exposed to endocrine disrupting compounds

This review discusses various methodologies that can be used to understand, at the gene level, the consequences to fish upon exposure to endocrine disrupting compounds (EDCs). Several approaches for measuring expression of gene transcripts are discussed, including directed approaches, such as Northern blotting and quantitative reverse transcriptase polymerase chain reaction (RT-PCR) as well as open-ended approaches, such as differential display RT-PCR, subtractive hybridizations, and gene arrays. Each of these systems has advantages and disadvantages, strengths and weaknesses. Conducting experiments with each of these methods provides important information about the molecular mechanisms that result from exposure to EDCs, information which can be used in risk assessment of polluted sites found in the environment.

Effect of UV screens and preservatives on vitellogenin and choriogenin production in male medaka (Oryzias latipes)

Ultra violet (UV) screens and preservatives are widely and increasingly used in cosmetics and pharmaceuticals. In the present study, we examined the estrogenicity of 4-methyl-benzylidene camphor (4-MBC), octyl-methoxycinnamate (OMC), and propyl paraben (n-propyl-p-hydroxy-benzoate; PP), among UV screens and preservatives, using male medaka (Oryzias latipes), in regard to production of vitellogenin (VTG) and choriogenin (CHG) which are known to be estrogen-responsive gene products. First, using a VTG enzyme-linked immunosorbent assay (ELISA) system, we determined the increase in VTG plasma concentration in medaka due to exposure to 4-MBC, OMC, and PP, and compared this concentration to the non-treated control. Next, we found increases in mRNA expression levels of VTG subtypes VTG-1 and VTG-2, and CHG subtypes CHG-L and CHG-H, in liver due to exposure to 4-MBC, OMC, and PP compared to the non-treated control. In addition, we also found increased mRNA expression levels of estrogen receptor (ER) alpha, among sex hormone receptors in the liver, due to exposure to 4-MBC, OMC, and PP compared to the non-treated control. In this study, we showed that 4-MBC, OMC, and PP have estrogenic activity in fish.

Eggshell and egg yolk proteins in fish: hepatic proteins for the next generation: oogenetic, population, and evolutionary implications of endocrine disruption

The oocyte is the starting point for a new generation. Most of the machinery for DNA and protein synthesis needed for the developing embryo is made autonomously by the fertilized oocyte. However, in fish and in many other oviparous vertebrates, the major constituents of the egg, i.e. yolk and eggshell proteins, are synthesized in the liver and transported to the oocyte for uptake. Vitellogenesis, the process of yolk protein (vitellogenin) synthesis, transport, and uptake into the oocyte, and zonagenesis, the synthesis of eggshell zona radiata proteins, their transport and deposition by the maturing oocyte, are important aspects of oogenesis. The many molecular events involved in these processes require tight, coordinated regulation that is under strict endocrine control, with the female sex steroid hormone estradiol-17beta in a central role. The ability of many synthetic chemical compounds to mimic this estrogen can lead to unscheduled hepatic synthesis of vitellogenin and zona radiata proteins, with potentially detrimental effects to the adult, the egg, the developing embryo and, hence, to the recruitment to the fish population. This has led to the development of specific and sensitive assays for these proteins in fish, and the application of vitellogenin and zona radiata proteins as informative biomarkers for endocrine disrupting effects of chemicals and effluents using fish as test organisms. The genes encoding these important reproductive proteins are conserved in the animal kingdom and are products of several hundred million years of evolution.